A conventional random access memory (RAM) is an electric charge based device. A conventional RAM is volatile and cannot store data if power is turned off. In contrast, a magnetoresistive random access memory (MRAM) is a magnetic field based device, is non-volatile, and utilizes less power than a conventional RAM.
An MRAM utilizes a difference in magnetic directions between two plates in an MRAM bit cell to store data. One plate in an MRAM bit cell is “pinned,” such that the magnetic direction is permanent. The other plate in the MRAM bit cell is “free,” and the magnetic direction of the free plate is changed to be parallel or anti-parallel to that of the pinned plate depending on the desired value of the MRAM bit cell.
If the two plates in an MRAM bit cell have the same magnetic direction, the electrical resistance of the MRAM bit cell is less than if the two plates have opposite magnetic directions. Values, such as a one or a zero may be assigned to the different levels of resistance. The electric resistance of an MRAM bit cell is measured to determine whether the MRAM bit cell has been set to a value of one or a value of zero.
The magnetic direction of the free plate is changed via a spin-polarized current passed adjacent to the free layer of the MRAM bit cell. Such devices are sometimes referred to as spin-electronic devices, or spintronic devices. Spintronic devices include, for example, spin-transfer torque (STT) and spin-orbit torque (SOT) magnetic memories.
A significant obstacle that impedes the widespread adoption of spintronic devices is their speed. The speed of a spintronic device, such as an STT or SOT memory, is limited by the switching time of the magnetization of the magnetic medium. Switching times of magnetic materials are typically on the order of hundreds of picoseconds (ps). For comparison, a metal-oxide-semiconductor field-effect transistor (MOSFET) transistor can have a switching delay as short as 5 ps. Thus, in order for magnetic-based memories to challenge charge-based memories in information technologies, it would be desirable to dramatically reduce the time it takes to write data to a magnetic bit cell.